Power factor correction for LED drivers

ABSTRACT

A power factor correction circuit, and methods of operation, is described, that can downconvert AC mains power to a lower power suitable for driving one or more LEDs. The power factor correction circuit can provide a regulated current, in a single-stage embodiment, and a regulated voltage, in a dual-stage embodiment. The power factor correction circuit can include an isolation transformer along with a switch for controlling downconversion. The power factor correction circuit can alternatively include a switch without isolation. Either way, the switch can have a duty cycle proportional to a desired downconversion from the AC mains signal, and can skip half cycles of the AC mains signal in order to reduce the downconverted output of the power factor correction circuit.

CLAIM OF PRIORITY UNDER 35 U.S.C. § 119

The present Application for Patent claims priority to ProvisionalApplication No. 62/305,445 entitled “POWER FACTOR CORRECTION FOR LEDDRIVERS” filed Mar. 8, 2016, and assigned to the assignee hereof andhereby expressly incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to LED drivers. In particular,but not by way of limitation, the present disclosure relates to systems,methods and apparatuses for power factor correction in LED drivers.

DESCRIPTION OF RELATED ART

Lighting comprises approximately 17.5% of global electricityconsumption. As the world transitions from incandescent to solid statelighting (SSL) technology (e.g., LED bulbs), utilities and governmentregulatory agencies worldwide are concerned that, as this large segmentof the consumption base switches to SSL, it will increase infrastructurecosts.¹ This is due to the reactive nature of LED-based solid statelighting (i.e., voltage and current not being in phase), which resultsin higher distribution currents that adversely affect power factor (PF)and, in turn create a larger demand on the power grid.¹http://www.ledlighting-eetimes.com/en/power-factor-and-solid-state-lighting-implications-complications-and-resolutions.html?cmp_id=71&news_id=222908451

Power factor is defined as the ratio of the reactive power to the realpower (i.e., the percentage of generated power can be used to do work).This basically means that for an equivalent real power consumed by ahighly reactive load, for example 5 W, the actual current that the gridneeds to supply to the load in order to provide the real power has to behigher than the real power by the power factor ratio. For the previous 5W example, for a load with a PF of 0.5, the grid needs to provide 2× thecurrent actually required by the load at any given time. When multipliedby tens of thousands of households and numerous SSL devices perhousehold, one sees how improvements in power factor can vastly reducethe amount of power that utilities need to generate per customer. Thisadverse impact on the power grid does not apply to incandescentlighting, which is purely resistive and has a unity power factor.

LEDs have a non-linear impedance as do their drivers, causing the powerfactor to be inherently low. In order to combat this, some LED driversare design to compensate for power factor, and may have a goal ofachieving a power factor as close to 1 or unity as possible. Solid statelighting that incorporates power factor correction can reduce the impactof the change from incandescent to LED based lighting by increasing thepower factor to near unity by adding circuitry to the LED driver thatcorrects for the reactive input impedance.

Utilities are not the only ones interested in LED drivers with highpower factor correction. Regulators have been working with utilitycompanies to enact rigid standards to control the impact of solid statelighting technology on the power grid. This is because, while LEDlighting reduces the theoretical power draw on the grid, if power factoris not adequately addressed, then some of the gains made by the switchto LED lighting may be lost inefficient power transfer (i.e., poor powerfactor correction for LED lighting).

Historically, incandescent bulbs have had near-perfect power factor.Therefore, solid state lighting is being held to a much higher powerfactor standard compared to legacy AC/DC incandescent power supplies. Inmost cases, power supplies are free from any form of power factorregulation for supplies rated up to 75 W. However, for solid statelighting, power factor regulations typically kick in for loads as low as5 W or below, thus covering the vast majority of LED bulbs. Therefore,there is a need in the art for better power factor correction in LEDdrivers.

SUMMARY OF THE DISCLOSURE

The following presents a simplified summary relating to one or moreaspects and/or embodiments disclosed herein. As such, the followingsummary should not be considered an extensive overview relating to allcontemplated aspects and/or embodiments, nor should the followingsummary be regarded to identify key or critical elements relating to allcontemplated aspects and/or embodiments or to delineate the scopeassociated with any particular aspect and/or embodiment. Accordingly,the following summary has the sole purpose to present certain conceptsrelating to one or more aspects and/or embodiments relating to themechanisms disclosed herein in a simplified form to precede the detaileddescription presented below.

Some embodiments of the disclosure may be characterized as a method ofoperating a power factor correction circuit to drive a dimmable solidstate lighting device. The method can include controlling downconversionof a voltage in the power factor correction circuit by periodicallyswitching a switch coupled between a high voltage rail and a ground railof the power factor correction circuit, where a duty cycle of the switchcorresponds to a ratio of input and output voltages from the powerfactor correction circuit. The method also can include identifying zerocrossings of power on the high voltage rail. The method also can includedetermining a period of the power from the monitoring. The methodfurther can include turning the switch off for half cycles of the periodto reduce average power output from the power factor correction circuit,where a frequency of the turning the switch off corresponds to a ratioof input to output power from the power factor correction circuit.

Other embodiments of the disclosure may also be characterized as amethod of operating a power factor correction circuit to drive adimmable solid state lighting device. The method can include controllingdownconversion of a voltage in the power factor correction circuit byperiodically switching a switch coupled between a high voltage rail anda ground rail of the power factor correction circuit, where a duty cycleof the switch corresponds to a ratio of input and output voltages fromthe power factor correction circuit. The method can yet further includeproviding a transformer circuit between the high voltage rail and theswitch to isolate a primary from a secondary side of the power factorcorrection circuit. The method can also include identifying zerocrossings of power before or after the transformer circuit or via asecond primary coil of the transformer circuit. The method can alsoinclude determining a period of the power from the monitoring. Themethod can also include turning the switch off for half cycles of theperiod to reduce average power output from the power factor correctioncircuit, where a frequency of the turning the switch off corresponds toa ratio of input to output power from the power factor correctioncircuit.

Other embodiments of the disclosure can be characterized as a powerfactor correction circuit. The circuit can include a power factorcorrection circuit input, a power factor correction circuit output, ahigh voltage rail, a ground rail, a switch, and a controller. The switchcan be coupled between the high voltage rail and the ground rail. Thecontroller can control switching of the switch at a duty cyclecorresponding to a downconversion ratio between a voltage at the inputand a voltage at the output. The controller can be programmed, coded, orwired to (1) control the downconversion by periodically switching theswitch; (2) identify zero crossings of power on the high voltage rail atan isolation transformer coupled between the high voltage rail and theswitch, or at the output; (3) determine a period of the power from themonitoring; and (4) turn the switch off for half cycles of the period toreduce average power output from the power factor correction circuit,where a frequency of the turning the switch off corresponds to a ratioof input to output power from the power factor correction circuit.

Other aspects of the disclosure can be characterized as anon-transitory, tangible computer readable storage medium, encoded withprocessor readable instructions to perform a method of operating a powerfactor correction circuit to drive a dimmable solid state lightingdevice. The method can include controlling downconversion of a voltagein the power factor correction circuit by periodically switching aswitch coupled between a high voltage rail and a ground rail of thepower factor correction circuit, where a duty cycle of the switchcorresponds to a ratio of input and output voltages from the powerfactor correction circuit. The method also can include identifying zerocrossings of power on the high voltage rail. The method also can includedetermining a period of the power from the monitoring. The methodfurther can include turning the switch off for half cycles of the periodto reduce average power output from the power factor correction circuit,where a frequency of the turning the switch off corresponds to a ratioof input to output power from the power factor correction circuit.

Other aspects of the disclosure can be characterized as anon-transitory, tangible computer readable storage medium, encoded withprocessor readable instructions to perform a method of operating a powerfactor correction circuit to drive a dimmable solid state lightingdevice. The method can include controlling downconversion of a voltagein the power factor correction circuit by periodically switching aswitch coupled between a high voltage rail and a ground rail of thepower factor correction circuit, where a duty cycle of the switchcorresponds to a ratio of input and output voltages from the powerfactor correction circuit. The method can yet further include providinga transformer circuit between the high voltage rail and the switch toisolate a primary from a secondary side of the power factor correctioncircuit. The method can also include identifying zero crossings of powerbefore or after the transformer circuit or via a second primary coil ofthe transformer circuit. The method can also include determining aperiod of the power from the monitoring. The method can also includeturning the switch off for half cycles of the period to reduce averagepower output from the power factor correction circuit, where a frequencyof the turning the switch off corresponds to a ratio of input to outputpower from the power factor correction circuit.

Yet other aspects of the disclosure can be characterized as a powerfactor correction circuit. The circuit can include a rectificationcircuit having an AC mains input and a rectified power output. Thecircuit can also include a regulated voltage output that can beconfigured to provide regulated voltage to a voltage to currentconverter configured to provide regulated current to one or more LEDs.The circuit can also include a switch having one side coupled to ground.The circuit can also include a transformer circuit having a primary sidecoupled between a non-grounded side of the switch and the rectifiedpower output of the rectification circuit, and a secondary side coupledto the regulated voltage output. The circuit can yet further include acontroller in communication with the switch. The controller can includea tangible computer readable storage medium, encoded with processorreadable instructions to perform a method for adjusting power at theregulated voltage output by controlling the switch. The method caninclude (1) periodically switching the switch, a duty cycle of theswitching controlling a full power output at the regulated voltageoutput; (2) measuring a period of a power signal before therectification circuit, between the rectification circuit and thetransformer circuit, or after the transformer circuit; and (3) turningthe switch off for half cycles of the period with a frequencyproportional to a desired reduction in the power output at the regulatedvoltage output.

Another aspect of the disclosure can be characterized as a systemincluding an AC mains input, a rectifier circuit, a power factorcorrection circuit, a voltage to current conversion circuit, acontroller circuit, a wireless radio, and one or more additionaldevices. The rectifier circuit can be coupled to the AC mains input andconfigured to rectify AC mains power into an oscillating signal with nonegative voltage. The power factor correction circuit can be coupled tothe rectifier circuit and configured to adjust the oscillating signalsuch that a power factor of an output from the power factor correctioncircuit is improved as compared to the oscillating signal. The voltageto current conversion circuit can be coupled between the power factorcorrection circuit and a first of one or more LEDs, the voltage tocurrent conversion circuit configured to convert the output from thepower factor correction circuit to a regulated current that drives theone or more LEDs. The controller circuit can be coupled to the powerfactor correction circuit and the voltage to current conversion. Thewireless radio can be coupled to the controller circuit and configuredto provide remote access and control to the power factor control circuitand the voltage to current conversion circuit. The one or moreadditional devices can be coupled to the output of the power factorcorrection circuit, and can be configured to receive regulated powerfrom the power factor correction circuit. These one or more additionaldevices may not need their own power factor correction circuitry. Theseone or more additional devices may be selected from the group consistingof: sensors, lighting drivers, user interface devices, and actuators.

Yet another aspect of the disclosure can include a system including twoor more LED lighting systems, and a gateway device. The gateway devicecan be configured for coupling to the Internet and having a radio andconfigured to be in wireless communication with the two or more LEDlighting systems. At least one of the LED lighting systems can includean AC mains input, a rectifier circuit, a power factor correctioncircuit, a controller circuit, a wireless radio, and one or moreadditional devices. The rectifier circuit can be coupled to the AC mainsinput and configured to rectify AC mains power into an oscillatingsignal with no negative voltage. The power factor correction circuit canbe coupled to the rectifier circuit and configured to adjust theoscillating signal such that a power factor of an output from the powerfactor correction circuit. The voltage to current conversion circuit canbe coupled between the power factor correction circuit and a first ofone or more LEDs. The voltage to current conversion circuit can beconfigured to convert the output from the power factor correctioncircuit to a regulated current that drives the one or more LEDs. Thecontroller circuit can be coupled to the power factor correction circuitand the voltage to current conversion circuit. The wireless radio can becoupled to the controller circuit and can be configured to provideremote access and control to the power factor control circuit and thevoltage to current conversion circuit. The one or more additionaldevices coupled to the output of the power factor correction circuit,and can be configured to receive regulated power from the power factorcorrection circuit. These one or more additional devices may not needtheir own power factor correction circuitry, and may be selected fromthe group consisting of: sensors, lighting drivers, user interfacedevices, and actuators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a system where various devices, such as LED drivers,sensors, user interfaces, and actuators, can wirelessly interface withthe Internet via a gateway and an internal network including the gatewayand one or more of the radio-enabled devices;

FIG. 2 illustrates a pair of LED drivers driving a pair of one or moreLED lights. Each LED driver includes a connection to an AC mains, arectification circuit, a power factor correction circuit, and a voltageto current converter;

FIG. 3 illustrates a plurality of devices, where only a first LED driveris coupled to an AC mains, and where only the first LED driver has arectification circuit and a power factor correction circuit;

FIG. 4 illustrates another plurality of devices;

FIG. 5 illustrates a method of operating a plurality of devices, such asLED drivers, using a single rectification circuit, a single power factorcorrection circuit, and a single connection to an AC mains;

FIG. 6 illustrates a power factor correction circuit that can correspondto the plots shown in FIGS. 7b and 8 b;

FIG. 7a illustrates plots of input current and PFC power output as afunction of time for two output states of an LED driver according totraditional methods of reducing output power from a PFC circuit;

FIG. 7b illustrates plots of input current and PFC power output as afunction of time for two output states of an LED driver according to anembodiment of a new LED driver;

FIG. 8a illustrates switching states and power outputs corresponding toFIG. 7 a;

FIG. 8b illustrates switching states and power outputs corresponding toFIG. 7 b;

FIG. 9 illustrates a method of operating a power factor correctioncircuit to provide various levels of power output while maintaining aconstant current draw from an AC mains;

FIG. 10 illustrates a power factor correction circuit according to oneembodiment of this disclosure;

FIG. 11 illustrates a method for operating a power factor correctioncircuit passing signals across a galvanic isolation boundary bypiggybacking a 60 Hz feedback signal passing through an optical isolatorthat spans the galvanic isolation boundary;

FIG. 12a illustrates a single-stage LED driver incorporating the powerfactor correction circuits discussed earlier the application;

FIG. 12b illustrates a dual-stage LED driver incorporating the powerfactor correction circuits discussed earlier the application;

FIG. 13a illustrates another view of a single-stage LED driver;

FIG. 13b illustrates another view of a dual-stage LED driver;

FIG. 14 illustrates another embodiment of a power factor correctioncircuit where feedback is provided from the primary side;

FIG. 15 illustrates another embodiment of a power factor correctioncircuit where feedback is provided from the primary side;

FIG. 16 shows an LED driver receiving AC mains power, P_(in), from an ACmains and providing regulated LED current to one or more LEDs;

FIG. 17 illustrates another variation of an LED driver;

FIG. 18 illustrates one embodiment of a dual-stage driver where thetransformer circuit is part of the second stage (voltage to currentconverter); and

FIG. 19 illustrates one embodiment of a block diagram depicting physicalcomponents that may be utilized to realize any of the controllers hereindisclosed.

DETAILED DESCRIPTION

The word “exemplary” is used herein to mean “serving as an example,instance, or illustration.” Any embodiment described herein as“exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

Preliminary note: the flowcharts and block diagrams in the followingFigures illustrate the architecture, functionality, and operation ofpossible implementations of systems, methods and computer programproducts according to various embodiments of the present disclosure. Inthis regard, some blocks in these flowcharts or block diagrams mayrepresent a module, segment, or portion of code, which comprises one ormore executable instructions for implementing the specified logicalfunction(s). It should also be noted that, in some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustrations, and combinations ofblocks in the block diagrams and/or flowchart illustrations, can beimplemented by special purpose hardware-based systems that perform thespecified functions or acts, or combinations of special purpose hardwareand computer instructions.

Integrated Wireless Radio and LED Driver

Known commercial and residential lighting systems sometimes includewireless radios (e.g., WIFI, ZIGBEE, Z-WAVE, etc.) to communicate with ahub, gateway, or directly with the Internet, thereby enabling remote andscheduled control of lights. Typically wireless radios and LED driversare separate devices and thus the combined systems are often bulky,complex, and costly. A first aspect of this disclosure is an LED driverthat includes a wireless radio as part of the LED driver rather than asa separate device.

FIG. 1 illustrates a system where various devices, such as LED drivers,sensors, user interfaces, and actuators, can wirelessly interface withthe Internet via a gateway 110 and an internal network including thegateway 110 and one or more of the radio-enabled devices 102, 104, 106,108. In this way, one or more users 114 can monitor and control lightswitches, motion sensors, powered window blinds, garage doors, doorlocks, cameras, etc. Similarly, utilities 116 (e.g., power, water, andgas companies) can remotely monitor and optionally control (with userauthorization) devices such as lights and HVAC controls.

Each of the radio-enabled devices 102, 104, 106, 108 can include adriver, where the drivers each include an integrated wireless radio. Thegateway 110 can also include a wireless radio, and wirelesscommunication connections can be made between a given device 102, 104,06, 108 and the gateway 110. The gateway 110 is in communication withthe Internet 112 either directly, or via one or more intermediarydevices, such as switches, routers, modems, etc. The gateway 110 caninterface between different communication protocols. For instance, thewireless signals may use ENOCEAN, ZIGBEE, Z-WAVE, BLUETOOTH, WIFI,and/or infrared (IR) to name a few non-limiting examples. The Internet112 may use TCP/IP, to name one non-limiting example. Thus, the gateway110 interfaces between the protocol used to communicate with theInternet 112, and the protocol used to wirelessly communicate with theradio-enabled devices 102, 104, 106, 108. In some cases, the gateway 110may be able to handle more than one wireless protocol. For instance, LEDdrivers 102 may communicate via Z-WAVE, while the actuators 108communicate via ENOCEAN. In another example, some actuators 108 may useENOCEAN while others use WIFI. In an embodiment, each LED driver 102 caninclude or have an attached accessory such as, but not limited to, asensor 104, user interface 106, or actuator 108. In an embodiment, eachLED driver 102, via power from a power supply, can supply power toaccessories of the LED driver 102 such as, but not limited to, a sensor104, user interface 106, or actuator 108. In some instances, this powercan be delivered to accessories of the LED driver 102 via a bus havingone or more data and power channels, where a battery backup system iscoupled to the bus, and may include a control circuit for receiving dataand sending data and instructions on the bus. The LED driver 102 mayalso be able to power any controller or microprocessor of any of thesensors 104, user interfaces 106, actuators 108, or other accessories.

The LED drivers 102 can each be coupled between the AC mains and one ormore LED lights. Often, LED drivers and the lights they drive aremanufactured and/or sold as a single hardware system, so those of skillin the art will appreciate that the illustrated and described LEDdrivers 102 may or may not include driven LED lights.

In an embodiment, the LED drivers 102 can each include two controlcircuits: one in the wireless radio translates data to a definedprotocol such as ENOCEAN, ZIGBEE, Z-WAVE, WIFI, etc., and onecommunicates with a feedback sensor in each LED driver 102 and collectsdata (e.g., run time, temperature, power usage, etc.). In someembodiments, a single control circuit can perform both duties.

Daisy-Chained Devices with a Single AC Mains Connection

Known commercial and residential lighting systems often include separaterectifying and power factor correction circuitry for each light. Asecond aspect of this disclosure is a system of lights and/or otherdevices (e.g., sensors) wherein one LED driver includes a rectifyingcircuit and power factor correction (PFC), while other devices coupledto the first or primary LED driver do not include rectifying circuitsand PFC. In particular, the PFC from the first or primary LED canprovide one or more regulated voltage outputs (controlled voltage;floating current) that are used to power and drive one or moreadditional devices (such as other lights, sensors, or lightingaccessories). In this way, a system of lights can be implemented whereonly a single rectification circuit and a single power factor correctioncircuit is needed for any number of lights. Additionally, since theoutput of the PFC is low voltage (e.g., 5V-50V), the wiring between theprimary LED driver and the additional devices is low voltage and thusless regulated than typical high voltage (e.g., 120V) connectionsbetween lights. As seen, such a system benefits from: (1) only requiringa single rectification circuit and PFC per system of lights; and (2)enabling low voltage connections between lights that would otherwiserequire high voltage connections therebetween.

FIG. 2 illustrates a pair of LED drivers driving a pair of one or moreLED lights. Each LED driver 202, 204 includes a connection to an ACmains 206, a rectification circuit 208, 210, a power factor correctioncircuit 212, 214, and a voltage to current converter 216, 218.

In contrast, FIG. 3 illustrates a plurality of devices, where only afirst LED driver 302 is coupled to an AC mains 304, and where only thefirst LED driver 302 has a rectification circuit 306 and a power factorcorrection circuit 308. The power factor correction circuit 308 providesthree different regulated voltages, V₁, V_(Logic), and V₂, where V₁ isprovided to further circuitry within the first LED driver 302, and V₂ isused to power the additional devices 310, 312, 314. In this way, theadditional devices can be manufactured without their own rectificationand power factor correction circuits.

Additionally, the first LED driver 302 can include a microcontroller 316with a wireless radio. The wireless radio can be used to communicatewith a gateway, such as the gateway 110 in FIG. 1. In the illustratedembodiment, the microcontroller 316 is powered by an output from thepower factor correction circuit 308. Further, in this case themicrocontroller 316 voltage, V_(logic), is different than V₁ and V₂.However, in other embodiments, the microcontroller 316 can be powered byanother power source. Additionally, in another embodiment, the voltageto the microcontroller 316 can be the same as V₁ and V₂ (see, forinstance, FIG. 4). The microcontroller 316 can include a data connection318 to a voltage to current converter 320, and can be configured tomonitor the voltage to current converter 320 and provide instructions tothe voltage to current converter 320. For instance, the microcontroller316 can instruct the voltage to current converter 320 to adjust itscurrent output, I_(LED), and thereby change a brightness of the one ormore LED lights 322. One implementation of this ability is for a utilityor user to monitor the brightness of the one or more LEDs 322 throughthe wireless radio of the microcontroller 316 and the data connection318. The user or utility can then control the brightness or powerconsumption of the one or more LEDs 322 via this same control path inresponse to the monitoring.

In some cases, each device 302, 310, 312, 314 can include its ownmicrocontroller and wireless radio. However, this embodiment shows asingle microcontroller 316 controlling each device 302, 310, 312, 314.For instance, if the additional devices 310, 312, 314 are other LEDdrivers, then the microcontroller 316 can include a data connection tothe voltage to current converter in each of the additional LED drivers.In this way, a single microcontroller 316 and a single wireless radiocan be used to enable remote and wireless monitoring and control of theadditional LED drivers. If the additional devices 310, 312, 314 areother than LED drivers, then the data monitoring and control from themicrocontroller 316 can monitor and control key aspects or circuitswithin those devices. For instance, with a light switch, themicrocontroller 316 can monitor a state of the switch and sendinstructions to flip a state of the switch. For an HVAC control device,the microcontroller 316 can monitor sensors of the HVAC control device,such as temperature, humidity, and user inputs to the HVAC controldevice, while at the same time being able to send commands to change thetemperature. These are just a few examples of the interactions betweenthe microcontroller 316 and the additional devices 310, 312, 314.

To provide multiple voltages from the power factor correction circuit308, the power factor correction circuit 308 can include a multi-taptransformer. Each tap can provide a separate voltage, for instance, V₁from the first tap, V_(Logic) from the second tap, and V₂ from the thirdtap. Each tap can include a different number of windings or otherproperty that allows each tap to provide a separate voltage. Where amulti-tap transformer or some other means of providing separate voltagesis not used, the power factor correction circuit 316 can provide asingle voltage output as seen in FIG. 4. In this case, there may be aneed to include additional voltage conversion circuits at each of theadditional devices and possibly at the microcontroller.

Although not illustrated, in some embodiments, the microcontroller 316can include one or more data connections to the power connection 324between the power factor correction circuit 308 and the voltage tocurrent converter 320. The microcontroller 316 can include one or moredata connections to an output from the voltage to current converter 320.Each of these optional data connections can be used to monitor V₁ andI_(LED) as well as other properties of the power both within and whenexiting the LED driver 302.

One can see that V₂ is provided to the first additional device 310 andthen to the second and third additional devices 312, 314 via internalcircuitry of those additional devices 312, 314. While this setup can bebeneficial in some situations, it is not required, and thus in otherembodiments, the voltage, V₂, may be provided directly to two or more ofthe additional devices 310, 312, 314.

FIG. 5 illustrates a method of operating a plurality of devices, such asLED drivers, using a single rectification circuit, a single power factorcorrection circuit, and a single connection to an AC mains. The methodincludes receiving AC power at an LED driver from an AC mains (Block502), rectifying the AC power to DC power (Block 504), and performingpower factor correction on the DC power (Block 506). The method 500 canthen provide a regulated voltage from the power factor correction to avoltage to current converter, a microcontroller, and one or more devicesexternal to the LED driver (Block 508). Alternatively, Block 508 caninclude providing multiple regulated voltages from the power factorcorrection to a voltage to current converter, a microcontroller, and oneor more devices external to the LED driver. Those of skill in the artwill appreciate that rectification can occur before or after thestep-down or downconversion aspect of power factor correction.

Power Factor Correction Circuit Adjustable Output Method

Known LED drivers typically include a power factor correction circuitwith a controllable power output as seen in FIG. 7a (right). Powerfactor is often dealt with during step down conversion, where a dutycycle of a switch in the step down circuitry corresponds to the stepdown ratio. However, since input voltage to an LED driver is fixed at120V (in the US) and 220V (in the EU and UK), when decreased output fromthe power factor correction circuit is desired, for instance whendimming is requested, the input current to the power factor correctioncircuit drops as seen in FIG. 7a (left). Such adjustment of the poweroutput is typically achieved via a reduced duty cycle of the switch suchas switch 618 in FIG. 6 or other switching means (e.g., switch modepower supply). As the switch's duty cycle is decreased, the averagepower out decreases (e.g., the decrease of P₁ to P₂ in FIG. 7a (right)).A reduction in the duty cycle of a switching means can be seen in FIG.8a (left) and the resulting reduction in average output power can beseen in FIG. 8a (right). This decrease also results in a lower currentdraw from the AC mains as seen in FIG. 7a (left). Unfortunately, asinput current decreases, the power factor correction circuit's (e.g.,602 in FIG. 6) ability to maintain a desired total harmonic distortion(THD) and power factor decreases (typically low THD and high powerfactor are desired). Thus, there is a need for an LED driver that canmaintain a desired THD and power factor when the LED driver reducescurrent to the LED light.

As noted above, FIG. 7a (left) illustrates a plot of input currentversus time for two output states of an LED driver according totraditional methods of reducing output power from a PFC circuit. Dashedlines show a first state (limited or no dimming), and solid lines show asecond state (greater dimming than the first state). FIG. 7a (right)illustrates a plot of output power from a power factor correctioncircuit versus time for the two different power states, where the powerfactor correction circuit receives a rectified version of the inputcurrent shown in FIG. 7a (left). One sees that the traditional PFCcircuit sees decreased input current when output power is reduced.

In contrast, FIG. 7b (left) illustrates a plot of input current versustime for two power states of a new LED driver according to an embodimentof this disclosure. FIG. 7b (right) illustrates a plot of output powerfrom a power factor correction circuit versus time for the two powerstates, where the power factor correction circuit receives a rectifiedversion of the input current shown in FIG. 7b (left). With the new LEDdriver and method of operation, power is reduced (e.g., LED output isdimmed) by turning a switching means (e.g., a switch mode power supply)within the power factor correction circuit (e.g., 618) off for one ormore half cycles of the input, causing the output power to fall from P₁to P₃, while maintaining an amplitude of the input current. Power in thePFC circuit is cut every other half cycle, leading to a reduced averagepower, P₃, yet maintaining the instantaneous input current during halfcycles where power is transmitted. Such a power reduction can be carriedout via a switch mode power supply or switching means within the PFCcircuit. Consequently, the power factor correction circuit is able toreduce power out while also accurately producing a desired THD and powerfactor since there is no reduction in input current when output power isreduced. FIG. 7b (right) illustrates an example where the PFC circuitcuts power every other half cycle, but in other instances, othermultiples of half cycles may be cut in order to achieve different levelsof power out reduction (e.g., two out of every three cycles, or everythird cycle, etc.).

The output power shown in FIG. 7b right can be measured, for instance,at an output of any of the following: 308 in FIG. 3; power factorcorrection in FIG. 4; 602 in FIG. 6; 1002 in FIG. 10; 1216 in FIG. 12a ;1266 in FIG. 12b ; 1316 in FIG. 13a ; and 1317 in FIG. 13b . Inputcurrent can be measured, for instance at input 604 in FIG. 6, oranywhere between an AC mains and the optional filter 608, or between theAC mains and the primary side of the transformer circuit 612 if theoptional filter 608 is not implemented on the primary side.

FIGS. 8a and 8b illustrate switching states (left) that achieve theinput currents of FIGS. 7a and 7b (left) and the output powers shown inFIGS. 7a and 7b (right) and FIGS. 8a and 8b (right). It should be notedthat the right hand plots in both FIGS. 7 and 8 are identical. FIG. 8ashows how the duty cycle of a switch within a traditional power factorcorrection stage can be reduced in order to cause a decrease in theaverage output power (e.g., from P₁ to P₂). FIG. 8b shows the switchingcycle according to the new LED driver of this disclosure. Instead ofreducing the duty cycle of a switching means within the PFC circuit, theduty cycle can be left the same, but the entire switching means, or PFCcircuit, depending on implementation, can be shut off on select halfcycles of the incoming AC waveform. In the illustrated embodiment, theswitching means, or the PFC circuit, is turned off every half cycle. Inthis way the instantaneous current drawn remains the same during periodswhen the switch or PFC circuit is on, yet the average output power isreduced from P₁ to P₃. If a larger output power reduction is desired,then the switching means or PFC circuit can be turned off for a greaterpercentage of half cycles. For instance, two out of every three halfcycles, or five out of every six half cycles, etc. If a smallerreduction in output power is desired, then the switching means or PFCcircuit can be turned off for a lesser percentage of half cycles. Forinstance, one out of every three half cycles, or one out of every sixhalf cycles, etc.

The initial duty cycle of the switch or switching means, before areduction in output power, can be selected to downconvert input power tooutput power. For instance, downconverting, 120V power to 24V. Whiletraditional PFC circuits adjust the duty cycle further to adjust foradjustments of the power output (e.g., dimming), this disclosuremaintains this initial duty cycle, but turns the switch or switchingmeans off for entire half cycles in order to achieve the sameadjustments in power output, but without reductions in instantaneousinput current.

Although FIGS. 7 and 8 addressed a situation where power is rectifiedbefore being downconverted, these charts apply equally well tosituations where power is downconverted before being rectified.

FIG. 6 illustrates a power factor correction circuit that can correspondto the plots shown in FIGS. 7b and 8b . The power factor correction(PFC) circuit 602 shows a detailed view of the PFC circuits illustratedin FIGS. 3 and 4. The PFC circuit 602 includes an input 604 forreceiving a rectified power signal from an optional rectifier circuit(not shown), and includes an output 606 for providing a regulatedvoltage, V_(out), or regulated current, I_(LED). These outputs can beused to indirectly or directly, respectively, drive one or more LEDs.However, in alternative embodiments, the input 604 can receivednon-rectified power, which is then downconverted, and rectified afterdownconversion, for instance via a rectifier coupled to the output 606.The PFC circuit 602 can optionally include a filter 608 and an optionalrectification and filter circuit 610. Either 602 or 608 can beimplemented. A transformer circuit 612 is arranged between the optionalfilter 608 and the optional rectification and filter circuit 610 orbetween the input 604 and the output 606. The transformer circuit 612provides galvanic isolation between the primary side (e.g., AC mainsside) and the secondary side (e.g., LED light side). Galvanic isolationis a principle of isolating functional sections of electrical systems toprevent current flow; in other words, no direct conduction path ispermitted from the primary to the secondary side. Thus, the galvanicisolation boundary 614 represents a boundary across which DC electricalcurrent is unable to cross. The galvanic isolation boundary 614 caninclude the transformer circuit 612, a gap between PCB boards, an airgap, and/or other mechanisms known in the art to achieve galvanicisolation. One can see that the primary side of the transformer circuit612 is on the left side of the galvanic isolation boundary 614, or the“hot” side of the boundary 614, and the secondary side of thetransformer circuit 612 is on the right side of the boundary 614, or theside that is considered relatively safe to human contact.

The PFC 602 can also include a controller circuit 616 arranged on andcoupled to the primary side. The controller 616 can be coupled to aswitch 618 or switching means that controls whether or not the primaryside of the transformer circuit 612 is coupled to ground or not. Thecontroller 616 may react to feedback from the secondary side of thetransformer circuit 612 (e.g., a voltage at an output of the transformercircuit 612). As noted above, electrical connections cannot cross thegalvanic isolation boundary 614, so to provide feedback to thecontroller 616 from the secondary side of the transformer circuit 612,an optical isolator 620 is implemented. The optical isolator 620 is anopto-electronic device having two electrical input/output interfaces622, 624. A first of these 622 can be coupled to the controller 616, anda second 624 can be coupled to an output of the secondary side of thetransformer circuit 612. Between these two interfaces 622, 624 is anoptical relay and an optical-to-electrical converter for each interface622, 624. The optical relay allows data to be optically transmittedacross the galvanic isolation boundary 614 without a physical electricalconnection. Sometimes an optical isolator 620 is a unidirectionaldevice, and in such cases, the optical isolator 620 can be configured toonly pass data toward the hot side of the galvanic isolation boundary614 (e.g., from interface 624 to interface 622).

In some embodiments, the controller 616 can include an optional data orcommunication channel 617 to another controller (not shown). Forinstance, the another controller could be configured to control chargingand discharging of an energy storage device that is charged from anoutput of the PFC circuit 602. The another controller could also beconfigured to control operation of a voltage to current converter thatconverts the output voltage, V_(out), of the PFC circuit 602, to aregulated LED current used to drive one or more LEDs. This anothercontroller, can be referred to as a master controller, since it can beconfigured to control other sub systems or other controllers within anLED driver. The master controller can be part of an LED driver thatincludes the PFC circuit 602, or can be coupled to but external to theLED driver.

While the switch 618 is typically used as part of a switch-mode powersupply and its duty cycle determines an output power from the secondaryside of the transformer circuit 612, here the switch 618 can becontrolled so as to effect a reduced output of the LED driver withoutdecreasing the duty cycle and thereby avoiding a reduction ininstantaneous input current at input 604. In particular, to change anaverage output power at output 606, the controller 616 can maintain aconstant duty cycle of the switch 618, but leave the switch 618 openduring select half cycles of input current. As a result, instantaneousinput current at input 604 remains the same regardless of output power,and average output power at output 606 can be reduced. Via thisswitching method, the PFC circuit 602 can operate as effectively as whenno power reduction (e.g., dimming) is taking place (i.e., where no halfcycles are chopped or switched out of the power output).

Additionally, power savings can be achieve where the controller 616 onlyswitches the switch 618 at zero crossings of the power. Power can bemeasured as power, voltage, current, or a combination of these at theinput 604, input of the transformer circuit 612, at the transformercircuit 612, at an output 613 of the transformer circuit 612, or at theoutput 606. The illustrated embodiment, shows this feedback coming froman output 613 of the transformer circuit 612, but in other embodiments,the feedback used to identify zero crossings of the power can use any ofthe above-mentioned feedback sources. For instance, FIG. 14 illustratesone non-limiting example where the feedback is provided from the primaryside of a transformer circuit 1412. In particular, feedback can beprovided via a second coil of the primary side of the transformercircuit 1412. In another example, FIG. 15 shows the feedback beingprovided from between the optional filter 1508 and the transformercircuit 1512 via a resistive element R₁.

The switch 618 can be implemented by a variety of devices or circuits,such as a physical relay or a transistor to name two non-limitingexamples. In some embodiments, more than one physical switch can beused, for instance, a MOSFET network may be implemented as the switch618.

One of skill in the art will recognize that the PFC circuit 602illustrates a functional diagram only rather than a circuit diagram, andthus other operative circuit configurations can be used to implement thesame functionality without departing from the scope of the disclosure.In other words, any PFC circuit topology can utilize this aspect of thedisclosure. For instance, the switch 618 can be replaced with two ormore switches. As another example, the transformer circuit 612 can bereplaced by other devices that can transfer power while providinggalvanic isolation.

FIG. 9 illustrates a method of operating a power factor correctioncircuit so as to provide various levels of power output whilemaintaining a constant current draw from an AC mains. The method 900includes operating a switch of a power factor correction circuit at aduty cycle greater than a frequency of AC mains power (Block 902). Thisduty cycle is selected to achieve a desired downconversion of the ACmains power. Said another way, the duty cycle is selected to achieve adesired regulated voltage output that is lower than the AC mainsvoltage. The method 900 can also include accessing a power output fromthe power factor correction circuit (Block 904) and selecting a newpower output for the power factor correction circuit (Block 906). Giventhe new power output, the method 900 switches the switch off duringselect half cycles of the AC mains power to achieve the new power output(Block 908). For instance, in order to cut the power output in half,every half cycle may see the switch turned off completely for a fullhalf cycle of each period.

Additionally, switching of the switch may be aligned with zero crossingsof the power, voltage, or current, measured on the primary side, thesecondary side, or within a transformer circuit of the PFC circuit.

Piggybacked Signal Through Optical Isolator of Power Factor CorrectionCircuit

As noted above, power factor correction circuits often require galvanicisolation to protect users from electrocution. In other words, the LEDlight can be electrically isolated from the 120V, or “hot” side of theLED driver by a means such as a transformer (where power passes from oneside of the transformer to the other via an electric field rather thanvia a physical conductive connection). Some LED drivers include anoptical isolator that spans the galvanic isolation and allows feedbackfrom the output or secondary side of the transformer to be passed backto a controller on the primary side of the transformer. This opticalisolator often carries an analogue signal centered around 60 Hz acrossthe galvanic isolation boundary that corresponds to the AC frequency ofthe AC mains power. Additional data cannot cross the galvanic isolationsince any electrical data connection requires a physical coupling acrossthe boundary, which would sever the galvanic isolation. However, theremay be additional data to be passed across the galvanic isolationboundary.

One solution is to add one or more additional optical isolators.However, since these optical isolators each include circuits for passingoptical signals between the two sides of the galvanic isolation, theycan be bulky and costly, and the use of additional optical isolators maynot be feasible or commercially viable.

To address these limitations in the art, this disclosure describes anembodiment of a PFC circuit including an optical isolator and furtherincluding a signal generator on the secondary side of the galvanicisolation boundary and a signal analyzer on the primary side of thegalvanic isolation boundary (see FIG. 10). The signal generator 1026 canpiggyback the 60 Hz feedback signal already traveling across the opticalisolator 1020, for instance with a 120 Hz signal, or another higherfrequency signal that is easily filtered or separated from the 60 Hzsignal, and in this way additional data can be passed across thegalvanic isolation boundary 1014 without the addition of one or moreadditional optical isolators. The signal analyzer 1028 can then look atthe signal coming through the optical isolator 1020 and filter out the60 Hz signal, thereby leaving the 120 Hz signal. This data can, forinstance, be provided to the controller 1016 to provide furtherinformation or feedback for use in controlling the power factorcorrection circuit 1002.

In some embodiments, a capacitor 1030, capacitive device, or other lowfrequency filtering circuit can be added to an input of the signalanalyzer in order to filter out the 60 Hz signal.

FIG. 11 illustrates a method for operating a power factor correctioncircuit passing signals across a galvanic isolation boundary bypiggybacking a 60 Hz feedback signal passing through an optical isolatorthat spans the galvanic isolation boundary. The method 1100 can includeproviding a 60 Hz analogue feedback signal across a galvanic isolationof a power factor correction (PFC) circuit via an optical isolator(1102). The method 1100 can further include mixing the 60 Hz signal witha 120 Hz or greater signal on the secondary side of the galvanicisolation (Block 1104). The method 1100 can further include receivingboth signals on the primary side of the galvanic isolation (Block 1106),and extracting the 120 Hz or greater signal and providing this extractedsignal to a controller on the primary side of the galvanic isolation(Block 1108). The 60 Hz signal can also be extracted and providedseparately to the controller.

In other embodiments, the 60 Hz and 120 Hz or greater signals can bereplaced by other frequencies.

Modular Power Factor Correction Circuit Configured for Use inSingle-Stage and Two-Stage Led Drivers

FIGS. 12a and 12b illustrate single-stage and two-stage LED driversincorporating the PFC circuits discussed above. The single-stage LEDdriver 1202 is coupled between an AC mains 1201 and one or more LEDlights 1204. The AC mains 1201 couples to an input 1206 of thesingle-state LED driver 1202, and this input 1206 is coupled to an input1208 of a rectification circuit 1210. The rectification circuit 1210 hasan output 1212 coupled to an input 1214 of a PFC circuit 1216. The PFCcircuit 1216 has an output 1218 that provides a regulated LED current,I_(LED). The PFC circuit's 1216 output 1218 is coupled to an output 1220of the single-stage LED driver 1202, which is coupled to the one or moreLED lights 1204 and provides the regulated LED current, I_(LED), to theone or more LED lights 1204.

In the two-stage LED driver 1250 (FIG. 12b ), the same components exist,but the PFC output 1268 provides a regulated voltage, V_(out), ratherthan a regulated LED current, and this output 1268 is coupled to aninput 1272 of a voltage to current converter 1274. The voltage tocurrent converter 1274 has an output 1276 that provides a regulated LEDcurrent, I_(LED), that is provided to an output 1270 of the two-stageLED driver 1250 and to one or more LED lights 1254.

Because the PFC circuits 1216, 1266 have different outputs depending onwhether the PFC circuit is part of a single-stage or two-stage LEDdriver, a different PFC circuit is needed for the two different types ofLED drivers 1202, 1250. However, costs could be reduced if the same PFCcircuit could be used for both single and dual stage LED drivers 1202,1250. In other words, for companies producing both single-stage andtwo-stage products, there is a need for a single PFC circuit that can beimplemented in either product.

This disclosure describes single and dual-stage LED drivers where asingle PFC circuit can be interchangeably used in either type of LEDdriver. FIGS. 13a and 13b illustrate embodiments of such a dual purposePFC circuit.

As with the LED drivers of FIGS. 12a and 12b , the single-stage LEDdriver 1302 is coupled between an AC mains 1301 and one or more LEDlights 1304. Again, the single-stage LED driver 1302 includes arectification circuit 1310 and a PFC circuit 1316, but in this case thePFC circuit 1316 of the single-stage LED driver is the same as the PFCcircuit 1316 of the two-stage LED driver 1350.

Further, the PFC circuit 1316 has two modes: a voltage mode foroutputting regulated voltage, V_(out), and a current mode for outputtingregulated LED current, I_(LED). The current mode is designed for use ina single-stage LED driver 1302 and the voltage mode is designed for usein a two-stage LED driver 1304. A controller 1336 in the PFC circuit1316 determines which output is desired, and directs the PFC circuit1316 to change to the corresponding mode so that its output matches theLED driver type that it is installed in.

To determine the type of LED driver, the controller 1336 acquires dataindicating some defining characteristic of the type of LED driver (e.g.,whether single or dual-stage). Everything on the primary side of thegalvanic isolation boundary is identical between the two drivers, andthus no indicators of driver type are available on the primary side.However, the secondary side includes components and feedback that canindicate the driver type. Yet, as noted earlier, it is not possible tocreate a physical electrical connection across this boundary, so thereis no known solution for conveying data indicating the driver type tothe controller 1336 from the secondary side.

Fortunately, and as discussed above, a signal with a frequency that doesnot interfere with the 60 Hz feedback signal on the optical isolator1330 can piggyback the 60 Hz feedback signal. With the use of a signalgenerator 1332 on the secondary side of the optical isolator 1330 and asignal analyzer 1334 on the primary side, a piggybacked signal canconvey to the controller 1336 whether the PFC circuit 1316 output iscoupled to a voltage to current converter 1374 or directly to the one ormore LED lights 1304; in other words, whether the LED driver issingle-stage or dual-stage and hence whether the PFC circuit 1316 shouldbe put into the current or voltage mode.

To generate the piggybacked signal, the signal generator 1352 canreceive an input, or “dual-stage indicator”, from the voltage to currentconverter 1374 when such a converter exists. When this occurs, thesignal generator 1352 can send a piggyback signal through the opticalisolator 1350 of the PFC circuit 1316, where this piggyback signal isadded to or combined with the existing 60 Hz feedback signal alreadypassing through the optical isolator 1350. A signal analyzer 1334 on theprimary side of the galvanic isolation boundary can receive thispiggyback signal and either inform the controller 1356 that the LEDdriver 1350 includes the voltage to current converter 1374, and allowthe controller 1316 to conclude that the LED driver is dual-stage, ormake the conclusion itself and inform the controller 1356 that the LEDdriver 1350 is a dual-stage driver. Either way, the controller 1356 canthen instruct the PFC circuit 1316 to output a regulated voltage,V_(out).

If a voltage to current converter is not present, then the signalgenerator 1352 either does not send a piggyback signal or sends adifferent piggyback signal indicating that no voltage to currentconverter is present. If the piggyback signal is passed through theoptical isolator 1350, then the signal analyzer 1334 receives andextracts this piggyback signal and tells the controller 1356 that avoltage to current converter is not present. The controller 1356 canthen instruct the PFC circuit 1316 to provide a regulated current,I_(LED). Alternatively, the signal analyzer 1334 can extract thepiggyback signal and pass it along to the controller 1356, which canthen analyze the extracted signal and conclude that a voltage to currentconverter is not present.

As seen, piggybacking the 60 Hz signal of the optical isolator 1330provides a way for the LED driver 1302, 1350 to inform the controller1356 of the PFC circuit 1316, what type of LED driver the PFC circuit1316 is installed in, and thereby allows a single PFC circuit 1316 to beused in both types of LED drivers 1302, 1350. Other LED drivers cannotachieve this modularity because they do not enable a simplecost-effective way to pass data over the galvanic isolation boundary.

In other embodiments, a master controller on the secondary side of thegalvanic isolation boundary, or separate from the LED drivers 1302, 1350can identify the type of driver and pass this info or an instruction tothe PFC circuit 1316, which can then select an output mode (e.g.,voltage or current regulating) based on this information or theinstruction from the master controller. Further details of embodimentswhere a master controller is implemented can be seen in U.S. Ser. No.15/453,772, which is hereby incorporated by reference in its entirety.

While this disclosure has described an LED of either the single ordual-stage variety, other variations can include active and passivemethods for power factor correction. Passive PFC solutions typicallyconsist of passive input filters and offer some cost benefits, but sincepassive PFC optimizes for a specific input voltage and currentcondition, when those conditions change, the power factor alsodecreases. In the case of dimmable luminaires, passive PFC may be notacceptable as the power factor can vary broadly across the fulloperating brightness range of the bulb. Sometimes active PFC is desiredto adequately maintain high PFC across load and line conditions.

FIG. 16-18 illustrate some examples of different implementations of theLED driver systems described herein. FIG. 16 shows an LED driverreceiving AC mains power, P_(in), from an AC mains 1602 and providingregulated LED current to one or more LEDs 1614. The AC mains power canoptionally be first rectified in rectification circuit 1604, althoughrectification can also occur after voltage regulation (or step down ofthe voltage). Once rectified, the power is delivered to a primary sideof a transformer circuit 1610. The primary side of the transformercircuit 1610 is also coupled to ground via a switch 1608 and one or moreresistive elements R₂. A controller 1606 is coupled to and controls theswitch 1608 and monitors feedback from a feedback coil 1612 on theprimary side. The controller 1606 can also monitor feedback from theinput to the transformer circuit 1610 via resistive element R₁. The dutycycle that the controller 1606 imparts to the switch 1608 isproportional to the voltage out on the secondary side of the transformercircuit 1610. The controller 1606 can monitor zero crossings of thesignal at the input to the transformer circuit 1610 or via the feedbackcoil 1612 and use this to determine when switching of the switch 1608 isto occur to minimize power losses. Also, the controller 1606 can receiveindications or instructions to reduce power to the one or more LEDs 1614(e.g., a dimming signal), and can turn the switch 1608 entirely off forselect half cycles of the monitored signal. Where the output of thetransformer circuit 1610 is provided to the one or more LEDs 1614, thedriver can be considered a single-stage driver. However, those of skillin the art will understand how to add an optional voltage to currentconverter 1620 (e.g., a current regulator) to the output of thetransformer circuit 1610 in order to form a dual-stage driver. Thesingle-stage variation offers lower cost, complexity, and size. However,the dual-stage variation reduces ripple and stress on any capacitiveelements between the transformer circuit 1610 and the one or more LEDs1614.

FIG. 17 illustrates another variation of an LED driver. Here, a bridgerectifier 1718 performs rectification of the AC mains signal, althoughonce again, the rectifier 1718 can be arranged on the secondary side ofthe transformer circuit 1710. A filter capacitor C₁ can be implementedbetween an output of the rectifier 1718 and ground. Feedback from afeedback coil 1712 on the primary side of the transformer circuit 1710can pass through a diode, D₂, and be filtered by capacitor C₃ inparallel with the diode, D₂. Between the transformer circuit 1710 andthe one or more LEDs 1714 a capacitor, C₂, and a resistive element, R₅,can be arranged in parallel between rails. Further, a diode, D₁, canlimit current direction to the one or more LEDs 1714.

It should be noted that the power factor correction circuits shown inFIGS. 6, 14, and 15 can be implemented in single-stage or dual-stagedrivers. Where a dual-stage driver is used, an output of the transformercircuits 612, 1412, and 1512 can be provided to a voltage to currentconverter or current regulator, which further smooths the output currentfor provision to one or more LEDs. Additionally, where a dual-stagetopology is used, the transformer circuit 612, 1412, or 1512 can bemoved to the voltage to current converter.

FIG. 18 illustrates one embodiment of a dual-stage driver where thetransformer circuit is part of the second stage (voltage to currentconverter). Here, the first stage includes rectification circuit 1804, acontroller 1806, and a switch 1808. The controller 1806 is coupled toand controls a switching of the switch 1808 to both achieve power factorcorrection and downconversion of the rectified power. However, the firststage does not provide isolation. The duty cycle of the switch 1808 cancontrol a voltage provided to the second stage, but the power providedto the second stage can also be reduced via turning the switch 1808 offfor select half cycles of the first stage power signal. The controller1806 can monitor zero crossings of the power in the first stage viavarious means including feedback from the rail through resistive elementR₁. The switch 1808 can be switched and turned on and off for cycleskips at the zero crossings identified by the controller 1806.

In the second stage a transformer circuit 1810 provides isolationbetween the high voltage primary side and the low voltage secondaryside, where the one or more LEDs 1814 are arranged. The transformercircuit 1810 can be coupled to an output of the first stage and toground through a second switch 1809 and a resistive element, R₇. Thesecondary side of the transformer circuit 1810 provides a stepped downvoltage to one or more LEDs 1814 through diode, D₁. The secondary sidealso includes a capacitor C₂ and a resistive element, R₅, in paralleland in parallel to the one or more LEDs 1814, and arranged between railsof the secondary side.

The methods described in connection with the embodiments disclosedherein may be embodied directly in hardware, in processor-executablecode encoded in a non-transitory tangible processor readable storagemedium, or in a combination of the two. Referring to FIG. 19 forexample, shown is a block diagram depicting physical components that maybe utilized to realize any of the controllers herein disclosed (e.g.,616, 1016, 1330, the controllers of FIGS. 14 and 16, 1606, 1706, 1806)according to an exemplary embodiment. As shown, in this embodiment anoptional display portion 1912 and nonvolatile memory 1920 are coupled toa bus 1922 that is also coupled to random access memory (“RAM”) 1924, aprocessing portion (which includes N processing components) 1926, anoptional field programmable gate array (FPGA) 1927, and a transceivercomponent 1928 that includes N transceivers. Although the componentsdepicted in FIG. 19 represent physical components, FIG. 19 is notintended to be a detailed hardware diagram; thus many of the componentsdepicted in FIG. 19 may be realized by common constructs or distributedamong additional physical components. Moreover, it is contemplated thatother existing and yet-to-be developed physical components andarchitectures may be utilized to implement the functional componentsdescribed with reference to FIG. 19.

The optional display portion 1912 generally operates to provide a userinterface for a user, and in several implementations, the display isrealized by a touchscreen display. In general, the nonvolatile memory1920 is non-transitory memory that functions to store (e.g.,persistently store) data and processor-executable code (includingexecutable code that is associated with effectuating the methodsdescribed herein). In some embodiments for example, the nonvolatilememory 1920 includes bootloader code, operating system code, file systemcode, and non-transitory processor-executable code to facilitate theexecution of a method described with reference to FIGS. 5, 9, and 11described further herein.

In many implementations, the nonvolatile memory 1920 is realized byflash memory (e.g., NAND or ONENAND memory), but it is contemplated thatother memory types may be utilized as well. Although it may be possibleto execute the code from the nonvolatile memory 1920, the executablecode in the nonvolatile memory is typically loaded into RAM 1924 andexecuted by one or more of the N processing components in the processingportion 1926.

The N processing components in connection with RAM 1924 generallyoperate to execute the instructions stored in nonvolatile memory 1920 toenable reduction in power output from a PFC circuit while maintaining aconstant input current (e.g., by switching a switch of a PFC circuit ata frequency greater than a frequency of an AC mains signal at an inputof the PFC circuit, and turning the switch off for select half cycles ofthe AC mains signal). For example, non-transitory, processor-executablecode to effectuate the methods described with reference to FIGS. 5, 9,and 11 may be persistently stored in nonvolatile memory 1920 andexecuted by the N processing components in connection with RAM 1924. Asone of ordinarily skill in the art will appreciate, the processingportion 1926 may include a video processor, digital signal processor(DSP), micro-controller, graphics processing unit (GPU), or otherhardware processing components or combinations of hardware and softwareprocessing components (e.g., an FPGA or an FPGA including digital logicprocessing portions).

In addition, or in the alternative, the processing portion 1926 may beconfigured to effectuate one or more aspects of the methodologiesdescribed herein (e.g., the methods described with reference to FIGS. 5,9, and 11). For example, non-transitory processor-readable instructionsmay be stored in the nonvolatile memory 1920 or in RAM 1924 and whenexecuted on the processing portion 1926, cause the processing portion1926 to perform methods for switching a switch of a PFC circuit. Inparticular, selecting a duty cycle that achieves a desired downcoversionof AC mains power to a voltage or current that can drive one or moreLEDs, while also turning the switch off for select half cycles of the ACmains signal in order to reduce a power provided to the one or more LEDs(e.g., for dimming purposes). Alternatively, non-transitoryFPGA-configuration-instructions may be persistently stored innonvolatile memory 1920 and accessed by the processing portion 1926(e.g., during boot up) to configure the hardware-configurable portionsof the processing portion 1926 to effectuate the functions of thecontrollers described earlier in this disclosure.

The input component 1930 operates to receive signals (e.g., the voltagefeedback from the secondary side of the transformer circuit of a PFCcircuit) that are indicative of one or more aspects of the output of thetransformer circuit of the PFC circuit. The signals received at theinput component 1930 may include, for example, voltage, current, power,or a combination thereof. The output component 1932 generally operatesto provide one or more analog or digital signals to effectuate anoperational aspect of the controllers disclosed earlier in thisdisclosure. For example, the output portion 1932 may provide the controlsignals for controlling the switch described with reference to FIGS. 6,10, 14-18.

The depicted transceiver component 1928 includes N transceiver chains,which may be used for communicating with external devices via wirelessor wireline networks. Each of the N transceiver chains may represent atransceiver associated with a particular communication scheme (e.g.,WiFi, Ethernet, Profibus, etc.).

As will be appreciated by one skilled in the art, aspects of the presentdisclosure may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present disclosure may take theform of an entirely hardware-based embodiment, an entirelysoftware-based embodiment (including firmware, resident software,micro-code, etc.) or an embodiment combining software and hardwareaspects that may all generally be referred to herein as a “circuit,”“module” or “system.” Furthermore, aspects of the present disclosure maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon.

As used herein, the recitation of “at least one of A, B and C” isintended to mean “either A, B, C or any combination of A, B and C.” Theprevious description of the disclosed embodiments is provided to enableany person skilled in the art to make or use the present disclosure.Various modifications to these embodiments will be readily apparent tothose skilled in the art, and the generic principles defined herein maybe applied to other embodiments without departing from the spirit orscope of the disclosure. Thus, the present disclosure is not intended tobe limited to the embodiments shown herein but is to be accorded thewidest scope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of operating a power factor correctioncircuit to drive a dimmable solid state lighting device, the methodcomprising: controlling downconversion of a voltage in the power factorcorrection circuit by periodically switching a switch, during switchingperiods, coupled between a high voltage rail and a ground rail of thepower factor correction circuit, where a duty cycle of the switchingcorresponds to a ratio of input and output voltages from the powerfactor correction circuit; identifying zero crossings of power on thehigh voltage rail; determining a period of the power from theidentifying; and turning the switch off during non-switching periodscomprising one or more consecutive half cycles of the period, thenon-switching periods interspersed between the switching periods, toreduce average power output from the power factor correction circuit,where a duty cycle of the non-switching periods corresponds to a ratioof input to output power from the power factor correction circuit;wherein a primary side of a transformer circuit is coupled between thehigh voltage rail and the switch and isolates an input from an output ofthe power factor correction circuit.
 2. The method of claim 1, whereininstantaneous input current to the power factor correction circuit doesnot decrease when the average power output from the power factorcorrection circuit is reduced.
 3. The method of claim 1, wherein theturning the switch off occurs at the zero crossings.
 4. The method ofclaim 1, wherein an output of the power factor correction circuitprovides regulated voltage to a current to voltage converter thatprovides regulated current to one or more light emitting diodes.
 5. Themethod of claim 1, wherein an output of the power factor correctioncircuit provides regulated current to one or more light emitting diodes.6. A method of operating a power factor correction circuit to drive adimmable solid state lighting device, the method comprising: controllingdownconversion of a voltage in the power factor correction circuit byperiodically switching a switch, during switching periods, coupledbetween a high voltage rail and a ground rail of the power factorcorrection circuit, where a duty cycle of the switching during switchingperiods corresponds to a ratio of input and output voltages from thepower factor correction circuit; providing a transformer circuit betweenthe high voltage rail and the switch to isolate a primary side from asecondary side of the power factor correction circuit; identifying zerocrossings of power before or after the transformer circuit or via asecond primary coil of the transformer circuit; determining a period ofthe power from the identifying; turning the switch off for non-switchingperiods comprising one or more consecutive half cycles of the period,the non-switching periods interspersed between the switching periods, toreduce average power output from the power factor correction circuit,where a duty cycle of the non-switching periods corresponds to a ratioof input to output power from the power factor correction circuit. 7.The method of claim 6, wherein instantaneous input current to the powerfactor correction circuit does not decrease when the average poweroutput from the power factor correction circuit is reduced.
 8. Themethod of claim 6, wherein the turning the switch off occurs at the zerocrossings.
 9. The method of claim 6, wherein an output of the powerfactor correction circuit provides a regulated voltage to a voltage tocurrent converter that provides a regulated current to one or more lightemitting diodes.
 10. The method of claim 6, wherein an output of thepower factor correction circuit provides a regulated current to one ormore light emitting diodes.
 11. A power factor correction circuit, thecircuit comprising: a power factor correction circuit input; a powerfactor correction circuit output; a high voltage rail; a ground rail; aswitch coupled between the high voltage rail and the ground rail; and acontroller controlling switching of the switch, during switchingperiods, at a duty cycle corresponding to a downconversion ratio betweena voltage at the power factor correction circuit input and a voltage atthe power factor correction circuit output, the controller programmed orwired to: identify zero crossings of power on the high voltage rail, atan isolation transformer coupled between the high voltage rail and theswitch, or at the power factor correction circuit output; determine aperiod of the power from the identifying; and turn the switch off fornon-switching periods comprising one or more consecutive half cycles ofthe period, the non-switching periods interspersed between the switchingperiods, to reduce average power output from the power factor correctioncircuit, where a duty cycle of the non-switching periods corresponds toa ratio of input to output power from the power factor correctioncircuit.
 12. The power factor correction circuit of claim 11, furthercomprising a transformer circuit coupled between the high voltage railand the switch.
 13. The power factor correction circuit of claim 11,wherein the power factor correction circuit output is configured tocouple to a voltage to current converter, which provides regulatedcurrent to one or more light emitting diodes.
 14. The power factorcorrection circuit of claim 11, wherein the power factor correctioncircuit output is configured to couple to one or more light emittingdiodes and provide a regulated current to the one or more light emittingdiodes.
 15. The power factor correction circuit of claim 11, furthercomprising an optical isolator for providing feedback from a secondaryside of a transformer circuit to the controller, wherein the feedback isused to identify the zero crossings.